19298-61-4Relevant academic research and scientific papers
Kinetic studies on the cobalt-catalyzed norbornadiene intermolecular Pauson-Khand reaction
Cabot, Rafel,Lledo, Agusti,Reves, Marc,Riera, Antoni,Verdaguer, Xavier
, p. 1134 - 1142 (2008/10/09)
The kinetics for the cobalt-catalyzed intermolecular Pauson-Khand reaction (PKR) between (trimethylsilyl)acetylene and norbornadiene (NBD) at a constant CO pressure has been studied by means of in situ FT-IR. The rate dependence on catalyst and substrate concentrations was examined, and it was found that the process is -1.9 order with respect to CO pressure, zero order with respect to acetylene, 0.3-1.2 order with respect to NBD, and 1.3 order with respect to the Co2(CO)8 catalyst. Catalytic reaction intermediates were examined by their corresponding metal carbonyl IR frequencies. By a one-pot consecutive Pauson-Khand experiment, the NBD-dicobalt hexacarbonyl complex was identified as a catalytically active complex. Co4(CO)12 was also studied as a catalyst source in the PKR. Analysis of the corresponding reaction intermediates by IR demonstrated that Co2(CO)8 and Co4(CO)12 provide identical intermediate profiles upon reaction with TMSC2H. The experimental measured kinetics are consistent with the alkene insertion being the rate-limiting step in the catalytic PKR. Finally, the effect of phosphine substitution on the catalyst and the use of Lewis acid additives were shown to have a deleterious effect on the reaction rate.
Photochemical and thermal reactions of Co2(CO)8 with Co2(CO)6(phosphine)2 compounds
Wegman, Richard W.,Brown, Theodore L.
, p. 183 - 186 (2008/10/08)
Dicobalt octacarbonyl reacts photochemically with dicobalt hexacarbonyl bis(phosphine), Co2(CO)6L2, to yield a photostationary equilibrium consisting of Co2(CO)8, Co2(CO)6L2, and Co2(CO)7L. The approach to such an equilibrium follows first-order kinetics. The kinetics of the process and the photostationary-state equilibrium constant are consistent with homolytic metal-metal bond cleavage in all the dimers, followed by bimolecular recombinations of the radicals to yield the three possible dinuclear species. Thermal reaction of Co2(CO)8 with Co2(CO)6L2 is slow in all cases except L = P(t-Bu)3, for which the reaction has a half-life of about 60 s. A mechanism involving electron transfer from the Co(CO)3L· radical to Co2(CO)8 is proposed for this relatively fast reaction.
